The present invention relates to a tin-base white metal bearing alloy improved in heat resistance and fatigue resistance.
In general, tin-base white metal bearing alloys comprise tin as a base metal to which Sb and Cu are added. Tin-base white metal bearing alloys usually have a composition of 5 to 13% Sb, 3 to 9% Cu, 0 to 4% Pb, and balance of Sn. Of such alloys, the alloys which do not contain Pb are employed for bearings for high-speed high-load application, e.g., bearings for diesel engines of marine vessels. However, the conventional white metal bearing alloys are not necessarily satisfactory in toughness, high-temperature strength, fatigue limit and so forth. In accordance with enlargement and power increase of diesel engines for marine vessels in recent years, there has been an increasing demand for enhancing toughness, high-temperature strength and fatigue limit of bearings.
White metal bearing alloys to answer this demand are disclosed in JP-B-45-17065 and JP-A-53-14614.
A tin-base white metal bearing alloy has a structure in which Cu.sub.6 Sn.sub.5 of acicular crystals structure (.epsilon.phase) and SbSn of cubic crystals structure (.beta.phase) are distributed over a soft matrix. The soft tin-base matrix exhibits an excellent surface property as a bearing and high conformability with respect to the surface of the associated rotary shaft. In addition, the above-mentioned hard compounds distributed over the soft matrix have favorable wear resistance and favorable load carrying capacity. With these properties being combined, the tin-base white metal bearing alloy serves as an excellent bearing alloy.
It is generally known that cracking in a bearing alloy occurs in relation to the tensile strength, the impact load resistance relates to the toughness, and growth of cracking mainly relates to the fineness of the structure. Therefore, occurrence of cracking can be prevented by increasing the tensile strength of the alloy, higher resistance to an impact load can be obtained by improving the toughness, and higher resistance to occurrence of cracking can be obtained by increasing the fineness of the structure.
From this point of view, in the white metal bearing alloy disclosed in JP-B-45-17065, Cd, Be and Cr are added to a tin-base white metal so as to enhance the tensile strength and toughness, and the fineness of the structure is increased to enhance the fatigue limit.
Also, in the white metal bearing alloy disclosed in JP-A-53-14614, Mn, Ni, Cr and Co are added to a tin-base white metal so as to enhance the tensile strength and toughness, and the fineness of the structure is increased to enhance the fatigue limit.
However, in the white metal bearing alloys disclosed in JP-B-45-17065 and JP-A-53-14614, the heat resistance is insufficient, the strength at high temperature is low, and the fatigue resistance is low. Consequently, it is difficult to use these bearing alloys for diesel engines of marine vessels which are remarkably increasing in size and power.